The eastern Ukrainian city of Donetsk has reportedly declared itself independent from the central government in Kiev and set a date for a referendum on joining Russia, according to local media reports.

The local government building was taken over on Sunday night by pro-Russian activists, and on Monday the Russian news agency Itar Tass reported that “members of the regional legislature” had moved to declare the city and its surrounds the Donetsk People’s Republic.

The Ukrainian prime minister denounced the creation of a separatist state, describing it as part of a Russian plan to invade the east of the country.

Arseniy Yatsenyuk told an emergency meeting of cabinet: “An anti-Ukrainian plan is being put into operation ... under which foreign troops will cross the border and seize the territory of the country.”

He added: “We will not allow this.”

In a series of developments which appear to show Donetsk following in the footsteps of Crimea, men purporting to be politicians at a session of the regional council said they had passed a piece of legislation entitled “An Act on State Sovereignty of the Donetsk People’s Republic”.

In the same session, legislators were also said to have passed a decision in favour of holding a referendum on joining the Russian federation, to be held “no later than 11 May”.

According to Itar Tass, the document sealing its independence will see Donetsk “build its relations in line with international law and on the basis of equality and mutual benefits”.

It added that “the territory of the republic within the recognized borders is indivisible and inviolable”.

The information was relayed to reporters outside by activists, who have barricaded the government buildings in anticipation of attempts by police to retake them.

Donetsk is the administrative centre of Ukraine’s heavily industrialised eastern region, the Donbas. The building of its Regional State Administration was seized last night by protesters chanting “Russia, Russia” and waving Russian flags.

It was not immediately clear how far the protesters had the support of Donetsk's legitimate regional leadership, but Mr Yatsenyuk blamed Russia for “destabilising” the region, referencing the reportedly vast accumulation of Russian troops stationed within 30km (19 miles) of the border.

There were fears Donetsk could be following in the footsteps of Crimea, already annexed by the Russian federation
In response on Monday afternoon, Russia's foreign ministry issued a statement calling for Kiev to stop blaming Moscow for the ongoing crisis.

“Stop nodding at Russia, blaming all the troubles of today's Ukraine on it,” it read, while also repeating demands for Ukraine to devolve further powers to its various regions.

Ukraine’s interior ministry said that on Sunday armed gunmen had occupied a security services building in Luhansk, a city some 25km (16 miles) west of Russia.

And the provincial government buildings of Kharkiv, Ukraine’s second-largest city, were reportedly also stormed briefly before being retaken.

On Monday, the German government said it was “very worried” about the weekend’s developments across eastern Ukraine.

Chancellor Angela Merkel's spokesman Steffen Seibert said: “The latest developments in Donetsk and in Kharkiv are something which we are all very worried about in the German government.

“We must urgently renew our appeal to all those in positions of responsibility to help stabilise the region and avoid such escalation.”